1. Field of the Invention
The present invention relates to a backlight apparatus used in, for example, a display apparatus, a lens used in the backlight apparatus, a light source unit, and a display apparatus equipped with the backlight apparatus.
2. Description of the Related Art
Currently, use of LEDs (Light Emitting Diodes) independent for each of R (red), G (green), and B (blue) has contributed to achieving an NTSC (National Television System Committee) ratio of 100% or more in backlights of a high color range used for liquid crystal panels. Therefore, commodification of the backlights in PCs (Personal Computers), amusement equipment, in-car equipment, and TVs is expected.
In a case of a middle- or large-sized backlight of 10 inches or more, for example, sufficient luminance and thinness are required to be compatible therein. Therefore, a new design of a direct LED backlight that has been employed in the middle- or large-sized backlights is required. The direct LED backlight refers to a backlight of a type in which a plurality of LEDs as a light source are arranged two-dimensionally and in parallel to a plane of the liquid crystal panel.
In the case of the direct LED backlight, the number of LEDs to be mounted varies depending on which of a power-type LED and a normal-type LED is used in relation to a light amount. When using the power-type LEDs, it is difficult to dispose the LED elements independent for each of R, G, and B close to each other due to the problem of the number, size, and heat of the LEDs. In other words, an increase in distances among the LED elements results in a disadvantage in mixing red light, green light, and blue light in a limited space. Also in this case, although not many problems are caused when a sufficient optical distance (thickness) can be secured, because it is currently difficult to bring the LED elements close to each other due to the move towards reductions in thickness, color variability is caused.
For reducing the thickness of the liquid crystal panel, side-emitting-type power LEDs of the related art are used in some cases. However, this case also has a limit in terms of color variability.
Meanwhile, when normal low-power LEDs are used, distances among RGB elements can be shortened. However, by merely using the LED elements as they are even when the distances are shortened, generation of color variability right above the LEDs cannot be avoided in a backlight assuming thickness reduction. Moreover, a large variation in RGB light distribution characteristics of the respective LED elements facilitates color variability, which is a large problem.
For solving the problem on such color variability, there is disclosed, for example, a device including a plurality of point light sources arranged one-dimensionally and a cylindrical lens disposed above the plurality of point light sources and elongated in the one dimensional direction (see, for example, Japanese Patent Application Laid-open No. 2006-286608 (paragraphs [0007] and [0009], FIG. 5); hereinafter, referred to as Patent Document 1). The cylindrical lens used in this device includes a concave lens function (52) in a direction vertical to a substrate holding the point light sources (y direction). Further, the cylindrical lens includes a convex lens function (54) in a part of the horizontal direction (x direction). With such a structure, light from the point light sources expands in a planar state even without a light guide plate, whereby color variability is prevented.